DC to DC (or DC/DC) converters are used to convert input DC (direct current) voltages to output DC voltages. Such converters may step down (buck) or step up (boost) the input DC voltages. The converter typically has a controller, a driver, a pair of switches, and an LC filter coupled to the pair of switches. The controller provides a control signal to the driver which then drives the pair of switches, e.g., a high-side switch and a low-side switch. The driver alternately turns each switch on and off thereby controlling the inductor current and the output voltage of the DC/DC converter. The controller typically utilizes a pulse-width modulation (PWM) signal to control the state of the high-side and low-side switches.
FIG. 1 shows a schematic diagram of a conventional DC/DC converter using multiple controllers 102_1-102_N. As illustrated in FIG. 1, multiple PWM signals are generated to control the states of several sets of switches (e.g., switches S11 and S12, switches S21 and S22, . . . , and switches SN1 and SN2), and each set of switches includes a high-side switch (e.g., the switch S11-SN1) and a low-side switch (e.g., the switch S12-SN2). Taking the controller 102_1 for example, if the PWM signal generated by the controller 102_1 is logic high, the high-side switch S11 is on and the low-side switch S12 is off. Thus, the inductor L1 is coupled to the input voltage source VIN, and the inductor current begins to ramp up. If the PWM signal is logic low, the high-side switch S11 is off and the low-side switch S12 is on. Thus, the inductor L1 is coupled to ground, and the inductor current begins to ramp down. Hence, the controller 102_1 can control the inductor current by controlling the duty cycle of the PWM signal.
In FIG. 1, currents flowing through the inductors L1-LN are controlled by controllers 102_1-102_N, respectively. More specifically, each controller 102_1-102_N receives a sense signal indicative of a corresponding inductor current from a corresponding sense resistor R1-RN. Each controller 102_1-102_N includes a comparator to compare the sense signal with a reference level, and controls the duty cycle of the PWM signal according to the comparison. In order to balance the inductor currents respectively flowing through the inductors L1-LN, the pulse widths of the PWM signals are required to be identical. However, due to non-ideality of analog circuits, e.g., the sense resistors R1-RN, comparators in the controllers 102_1-102_N, etc., the controllers 102_1-102_N may not be able to control the pulse widths of the PWM signals to be identical.
Accordingly, there is a need in the art for DC/DC converters that better control pulse width for each of the generated PWM signals.